reap

A tool for parsing Ruby heap dumps.

Builds a dominator tree from the reference graph showing which objects are holding on to large quantities of memory.

(Node v "dominates" node w in a directed graph if all paths from a given root to w run through v. In the context of memory references, this implies that object v is only live because object w is live.)

Supports drilldown into subtrees and optional graphical output.

Use

Basic usage:

```sh $ cargo run -q --release -- /tmp/heap.json -d out.dot -n 3 Object types using the most live memory: Thread: 2.1 MB (40 objects) String: 462.6 KB (9235 objects) Class: 223.7 KB (287 objects) ...: 653.0 KB (5909 objects)

Objects retaining the most live memory: root: 3.4 MB (15472 objects) Thread[0x7f83df87dc40]: 1.1 MB (25 objects) Thread[0x7f83e107cd78]: 1.0 MB (7 objects) ...: 4.6 MB (59857 objects)

Objects unreachable from root: Class: 189.6 KB (617 objects) String: 81.8 KB (1174 objects) ARRAY: 38.6 KB (298 objects) ...: 91.5 KB (1422 objects)

Wrote 33 nodes & 32 edges to out.dot ```

Dig into a subtree (in this case, the larger Thread):

```sh $ cargo run -q --release -- /tmp/heap.json -d out.dot -n 3 -r 0x7f83df87dc40 Object types using the most live memory: Thread: 1.0 MB (1 objects) Class: 1.6 KB (3 objects) Hash: 1.3 KB (7 objects) ...: 980 B (14 objects)

Objects retaining the most live memory: Thread[0x7f83df87dc40]: 1.1 MB (25 objects) Hash[0x7f83e10452d8][size=5]: 1.2 KB (6 objects) Object[0x7f83df8d62c8][CLASS]: 992 B (8 objects) ...: 3.0 KB (24 objects)

Objects reachable from, but not dominated by, 0x7f83df87dc40: String: 352.3 KB (6604 objects) Class: 220.6 KB (283 objects) Regexp: 108.8 KB (139 objects) ...: 465.2 KB (5716 objects)

Wrote 1 nodes & 0 edges to out.dot ```

Run with --help for full options.

Getting a heap dump

If you have rbtrace installed, and required in the process you're planning to trace, you can run:

sh rbtrace -p $PID -e "Thread.new{require 'objspace';f=open('/tmp/heap.json','w');ObjectSpace.dump_all(output: f, full: true);f.close}"

Otherwise, you can connect to the Ruby process with gdb, then run:

gdb call rb_eval_string_protect("Thread.new{require 'objspace';f=open('/tmp/heap.json','w');ObjectSpace.dump_all(output: f, full: true);f.close}", 0)